Goods and services tax, often known as GST, is a broad-based tax of 10% on most goods, services and other items sold or consumed in Australia. You will need to charge the GST and you can claim it back on many inputs into your business.

A company can register for GST if it is carrying on an enterprise. It can do this on the ABN application form. A company must be registered for GST if its annual GST turnover is $75,000 or more. The registration threshold for non-profit organisations is $150,000. There is a calculator here to assist with working out if you will pass the threshold https://www.ato.gov.au/Business/GST/Registering-for-GST/#WorkingoutyourGSTturnover1

If you don’t register for GST you cannot include/collect GST on your invoices. If you discover you will turnover more than the threshold you have 21 days to register.